The tournament final on Saturday is guaranteed to have at least one American female in it, as two-time U.S. Open champion and No. 9 Venus Williams will face Sloane Stephens in Thursday's semifinals.

"It's definitely the first-strike kind of tennis, I think is the easiest way to simplify it", said Vandeweghe of facing the No. 1 player.

Muguruza, who lost in the fourth round of the US Open to Czech 13th seed Petra Kvitova, becomes the 24th woman to top the rankings in WTA history. As a result, Garbine Muguruza of Spain will claim the top spot in the sport next week when the new rankings are released.

Pliskova had been the runner-up in 2016 and her failure to defend those points means that Wimbledon champion Muguruza will take the top ranking for the first time despite the Spaniard losing in the last 16 in NY. She was up against fellow big server Vandeweghe, who herself was looking to book her place in the semi finals of a grand slam for the first time in her career.

There were signs that the Vandeweghe backhand was beginning to falter but another heavy forehand return gave her a break at the start of the tie-break, and she served it out clinically from there.

However, Pliskova was able to break back and take a 5-4 lead.

Karolina Pliskova's eight-week run as world number one ended Wednesday with a US Open quarter-final loss, the Czech standout saying nothing has changed for her after so short a reign.

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This will mark the fifth meeting between Pliskova and Vandeweghe, with each taking two wins to date.

The win was Vandeweghe's second this year over the world's No. 1 player, in addition to topping Angelique Kerber in straight sets of the Australian Open.

Vandeweghe took the match in fitting fashion: with her serve.

The first came and went, but the American would earn another chance at victory. Pliskova has won seven of her last eight matches on hard court. Now, however, all eyes will be on Madison Keys as she tries to guarantee an American US Open champion - with two rounds left to play.

Pliskova never quite found her groove at Flushing Meadows this year as her ferocious serve lacked its usual bite.

As of now, there is a chance of an all American final. Sloane Stephens and Venus Williams will meet in one semi-final, while Vandeweghe now awaits the victor of Wednesday's match between compatriot Madison Keys and Kaia Kanepi. It is a great tournament for American tennis, especially with Serena Williams absent.